Jamming doesnt make it appear in a different location, it just blocks the signal. The aircraft IRU would keep the aircraft on track, with a drift rate. Drift rates are measured in nm/hour.
Aircraft traveling in certain areas of the world frequently lose SAT GPS coverage, or dont have enough SAT's available for horizontal and vertical location...there is the RAIM prediction for this.
On an aircraft, there are usually at least 3 GPS ant, located as far away from each other as possible. If you had a jammer on board the ac, it would still be difficult to block all of the antennae, and even if you did, the IRU would take over and provide aircraft position.